Photography is a popular method for people to record and remember their memories of past experiences. Photographic images can be captured by a photographic film or a solid state image sensor. Film-based photography is an analog process. An optical system forms an image of a scene on a film coated with a photosensitive material, most commonly silver halide emulsion grains. The exposure to photons activates a photochemical process in the silver halide emulsion grains, producing a latent image of the scene on the film. A latent image carries the information of the scene image, but it is not visible to human eyes. Subsequent development of the film containing the latent image can produce a visible image formed by dye molecules. The dye image on the photographic film can then be reproduced on a photographic paper. The exposed photographic films can be developed either in a central location, typically referred as a Central Lab, or a distributed site, which can be called as either a Minilab or a Microlab depending on the size and the throughput of the site. The traditional development and printing processes of the silver halide films, as described above, all involve wet chemical and analog processes. With the advancement of computer and imaging technologies in recent years, a demand has been created to provide users digital photographic services. By using digital methods, photographic images can be more readily received from and provided to users in various digital formats.
One problem that has arisen from the usage of digital images is the detection of the unauthorized use of copyrighted or personal images. It is known that the professional photographers have been greatly concerned about the illegitimate use of their copyrighted images in the recent years. As the use of Internet and digital imaging devices become more popular, this concern will spread to the common consumers.